1. Field of the Invention
The present invention relates to a RAID apparatus and a control method therefor.
2. Description of the Related Art
A disk array system includes a plurality of disk devices and one disk control device or a plurality of disk control devices. Systems each having the plurality of disk control devices include a system in which a disk device in charge of access is predetermined.
A known function which dynamically enlarges a capacitance of a logical unit (LU) is an LU concatenation function. The LU concatenation function not only simply concatenates LUs to each other but also performs stripe concatenation to allocate stripes to another physical disk.
FIG. 8 is a diagram illustrating a conventional RAID apparatus 41 in stripe concatenation. The RAID apparatus 41 includes a plurality of disk devices 42 and 43 and controller modules CM0 and CM1 that are in charge of access to the disk devices 42 and 43. The controller modules CM0 and CM1 have cache memories 44 and 45, respectively.
The controller module CM0 is in charge of access to the disk device 42 of RAID group 0, and the controller module CM1 is in charge of access to the disk device 43 of RAID group 1. In the cache memory 44 of the controller module CM0, for example, cache data of logical units of logical unit numbers LUN0, LUN1, and LUN2 are stored. In the cache memory 45 of the controller module CM1, cache data of logical units of logical unit numbers LUN3, LUN4, and LUN5 are stored.
LU concatenation is performed, and a stripe concatenation volume includes logical units of the logical unit numbers LUN0, LUN1, LUN3, and LUN4. Thereafter, when a host computer (not shown) sends an I/O request to the concatenated volume, stripes S1, S2, S3, S4, S5, S6, S7, and S8 sequentially access the concatenated volume in the order named. At this time, since the cache data of the logical units are stored in the cache memory 44 or 45 of the in-charge controller module CM0 or CM1, communication must be frequently performed between in-charge controller modules of respective RAID groups in an I/O process to the concatenated volume. The capability to access a stripe concatenated volume, in particular, the capability to access to the volume when a cache is hit, is considerably deteriorated.